Conventionally, through advances in charge coupled device (i.e., CCD) manufacturing technology, the size of a pixel has become smaller and the number of pixels in an array has increased. As a result of these advances, high density image sensors that employ CCDs have come to be used in electronic still cameras and other small CCD cameras.
Photographic lenses as set forth in Japanese Laid Open Patent Application H5-157962 and in Japanese Laid open Patent Application H11-125767, for example, are known to respond to such demands. The former application is a front-shutter-type photographic lens composed of four lens groups totaling five lens elements, with a stop positioned on the object side of the first lens group, and the latter application is a photographic lens composed of two lens groups totaling six lens elements, with a stop positioned between the first lens group and the second lens group.
High quality imaging is important for imaging lenses that are to be used in CCD cameras. Moreover, there is currently a strong demand for reduction in size and lower costs for such cameras. In recent years, CCDs have been widely used in digital cameras, but in the future, CCDs are expected to be incorporated into thin devices such as clocks, handheld tools such as mobile phones, and electronic notepads. In order to be used in such types of thin devices, a photographic lens that has a short overall length will become crucial. Thus, a photographic lens having optical properties that are substantially equivalent to the optical properties of conventional lenses, while further reducing the number of components so as to reduce the size and to lower costs, is in great demand.
The present invention relates to a single focus lens having a short overall length that is suitable for use in small photographic devices and which provides high quality images. More particularly, the present invention is a single focus lens made of only four lens components, preferably four lens elements, thereby providing a low cost lens which has its aberrations favorably corrected and is particularly suited for use in digital cameras.